Mass loss and macroinvertebrate colonisation of Pacific salmon carcasses in south-eastern Alaskan streams

1. We examined the spatial and temporal dynamics of pink salmon (Oncorhynchus gorbuscha) carcass decomposition (mass loss and macroinvertebrate colonisation) in southeastern Alaskan streams. Dry mass and macroinvertebrate fauna of carcasses placed in streams were measured every two weeks over two months in six artificial streams and once after six weeks in four natural streams. We also surveyed the macroinvertebrate fauna and wet mass of naturally occurring salmon carcasses. 2. Carcass mass loss in artificial streams was initially rapid and then declined over time (k = -0.033 day(-1)), and no significant differences were found among natural streams. 3. Several macroinvertebrate taxa colonised carcasses, but chironomid midge (Diptera: Chironomidae) and Zapada (Plecoptera: Nemouridae) larvae were found consistently and were the most abundant (on average 95 and 2%, respectively, of the invertebrates found). Chironomid abundance and biomass increased over time, whereas Zapada abundance and biomass did not. Significant differences in abundance were found among natural streams for Baetis (Ephemeroptera: Baetidae) and Sweltsa (Plecoptera: Chloroperlidae) larvae, while no significant differences were found for chironomid and Zapada abundance or biomass. 4. Our results suggest that salmon carcasses initially undergo a high rate of mass loss that tapers off with time. Chironomid and Zapada larvae are likely to be important in mediating nutrient and energy transfer between salmon carcasses and other components of the freshwater-riparian food web in south-eastern Alaskan streams.